Thick and thin polyester multifilament yarn

ABSTRACT

A thick and thin polyester multifilament yarn having an excellent natural fiber yarn-like hand, a dry touch and spun yarn-like appearance includes a plurality of individual thick and thin polyester multifilaments varying in thickness along the longitudinal direction thereof and exhibits a spectrum having a first peak (Pmax 1 ) of a coefficient of variation in yarn thickness of 4 to 10 cm, a second peak (Pmax 2 ) of the yarn thickness variation coefficient of 50 to 150 cm and a ratio (Pmax 1 /Pmax 2 ) of 1.5 to 4.0, measured by the normal mode test method using the Uster evenness tester.

TECHNICAL FIELD

[0001] The present invention relates to a thick and thin polyestermultifilament yarn. More particularly, the present invention relates toa thick and thin polyester multifilament yarn having a naturalfiber-like or filament yarn-like hand, a dry touch and a spun yarn-likeappearance.

BACKGROUND ART

[0002] It is well known that when an undrawn polyester multifilamentyarn is incompletely drawn, a thick and thin polyester multifilamentyarn is obtained. In this thick and thin multifilament yarn, with anincrease in the unevenness in the thickness of the yarn, naturally, thespecial hand of the yarn is enhanced. If the unevenness in the thicknessof the yarn is too high, a problem, that the resultant yarn isdisadvantageous in that the natural multifilament yarn-like hand of theyarn is deteriorated and the easy handing and mechanical properties ofthe yarn are degraded due to the presence of the undrawn portion havinga low degree of orientation in the filaments, occurs.

[0003] To solve the above-mentioned problem, Japanese Examined PatentPublication No. 3-77304 discloses a thick and thin filament yarn inwhich the thick portions of the individual filaments are specificallydispersed and in which a thickness value, at a yarn thickness variationperiod of 50 cm, in a spectrogram obtained by the normal mode test usingthe Uster unevenness tester, is ½ or less of the maximum value of theyarn thickness. It is true that the thick and thin filament yarn of theJapanese publication exhibits enhanced mechanical property and handlingproperty. However, the hand of the thick and thin filament yarn may beunsatisfactory for a certain use, and thus further improvement of theyarn, in the natural fiber or filament yarn-like hand, the dry touch andthe spun yarn-like appearance, is strongly desired.

SUMMARY OF THE INVENTION

[0004] The present invention was made on the basis of theabove-mentioned background art.

[0005] An object of the present invention is to provide a new thick andthin polyester multifilament yarn having an excellent natural fiber orfilament yarn-like hand, a good dry touch and a spun yarn-likeappearance.

[0006] The above-mentioned object can be attained by the thick and thinpolyester multifilament yarn of the present invention which comprises aplurality of thick and thin polyester individual filaments, thethickness of which periodically varies along the longitudinal directionthereof, wherein when the thick and thin multifilament yarn is subjectedto a yarn thickness variation measurement by the normal mode test methodusing the Uster evenness tester, the resultant spectrogram of the thickand thin multifilament yarn exhibits a first peak (P_(max1)) of thecoefficient of variation in yarn thickness at a thickness variationperiod of 4 to 10 cm and a second peak (P_(max2)) of the coefficient ofvariation of the yarn thickness at a thickness variation period of 50 to150 cm, and the ratio (P_(max1)/P_(max2)) of the first peak coefficientof variation in the yarn thickness (P_(max1)) to the second peakcoefficient of variation in the yarn thickness (P_(max2)) in the rangeof from 1.5 to 4.0.

[0007] The thick and thin polyester multifilament yarn of the presentinvention preferably exhibits, in the spectrogram of the thick and thinmultifilament yarn, a ratio (P_(max1)/P₂₀) of the first peak coefficientof variation in the yarn thickness (P_(max1)) to a coefficient ofvariation in the yarn thickness at a thickness variation period of 20 cm(P₂₀) in the range of 1.5 to 4.0.

[0008] In the thick and thin polyester multifilament yarn of the presentinvention, preferably, the individual thick and thin multifilaments havethick portions having a length in the range of 1 to 15 mm, and the thickand thin multifilament yarn has a U %, which is a mean yarn thicknessunevenness represented by a ratio in % of the mean deviation to the meanvalue of the yarn thickness, of 3.5% or more, as determined by thenormal mode test method using the Uster evenness tester at a yarn speedof 400 m/min at a twist number of 5500 turns/min for one minute.

[0009] The thick and thin polyester multifilament yarn of the presentinvention, preferably, has a shrinkage in boiling water of 10% or less.

[0010] In the thick and thin polyester multifilament yarn of the presentinvention, preferably, the individual thick and thin multifilaments eachhave a triangular cross-sectional profile.

[0011] In the thick and thin polyester multifilament yarn of the presentinvention, the individual thick and thin multifilaments preferablycontain a fine pore-forming agent mixed into a matrix consisting of apolyester resin.

[0012] In the thick and thin polyester multifilament yarn of the presentinvention, the fine pore-forming agent preferably comprises a metal saltcompound represented by the general formula (I):

[0013] in which formula (I), M¹ and M², respectively and independentlyfrom each other, represent a metal atom, R represents a hydrogen atom oran ester structure-forming functional group and n represents an integerof 1 or 2.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a spectrogram of an embodiment of the thick and thinpolyester multifilament yarn of the present invention, obtained by thenormal mode test using the Uster unevenness tester, showing arelationship between the yarn thickness variation period and thecoefficient of variation in yarn thickness of the yarn,

[0015]FIG. 2 is a spectrogram of an embodiment of conventional thick andthin polyester multifilament yarn obtained by the same test as mentionedabove.

BEST MODE OF CARRYING OUT THE INVENTION

[0016] The thick and thin polyester multifilament yarn of the presentinvention will be explained in detail below.

[0017] The polyester usable for the present invention is principallyselected from polyethylene terephthalates having repeating unitsconsisting of ethylene terephthalate groups, and optionally frompolyethylene terephthalate-copolymerized polyesters in which at leastone additional component, usually in a small amount of 15 molar % orless, preferably 10 molar % or less, still preferably 5 molar % or less,based on the molar amount of all the recurring units is copolymerized.

[0018] The polyester resin usable for the present invention may containan additive, for example, a delusterant. Particularly, the polyesterresin preferably contains a fine pore-forming agent for forming finepores or grooves on the surfaces of, or inside, the filaments when thefilaments are subjected to a weight-reduction treatment with an alkali,because the water-absorbing property, the natural fiber or filamentyarn-like hand, a brightness and a dry touch of the resultant filamentyarn can be improved in response to the form, size and distribution ofthe pores or grooves.

[0019] For example, when the polyester resin contains, as a finepore-forming agent, a sulfonate metal salt represented by the followinggeneral formula (I),

[0020] in which formula (I), M and M¹, respectively and independentlyfrom each other, represent a metal atom, preferably a member selectedfrom alkali metal, alkaline earth metal, manganese, cobalt and zincatoms, R represents a hydrogen atom or a ester-formable functionalgroup, and an represents an integer of 1 or 2, the resultant polyestermultifilament yarn exhibits an improved dry touch and cotton fiberyarn-like properties.

[0021] The above-mentioned sulfonate metal salt is preferably selectedfrom those disclosed in Japanese Examined Patent Publication No.61-31231. Particularly, 3-sodium 3-carboxybenzenesulfonate-5-sodiumcarboxylate, and 3-sodium hydroxyethoxycarbonylbenzenesulfonate-5-½magnesium carboxylate are usable.

[0022] The addition of the above-mentioned sulfonate metal salt to thepolyester resin can be carried out at any stage before melt-spinningstep of the polyester resin. For example, the sulfonate metal salt ismixed into the materials for the synthesis of the polyester or addedduring the synthesis procedure of the polyester.

[0023] The amount of the sulfonate metal salt to be added to thepolyester is preferably 0.5 to 2.5% by weight, more preferably 0.6 to1.2% by weight, based on the weight of the polyester. If the content ofthe sulfonate metal salt is too low, the resultant polyester filamentsmay exhibit an unsatisfactory cotton fiber-like hand, and if it is toohigh, the melt spinning procedure of the resultant polyester resincomposition may be troublsome.

[0024] In the present invention, the spectrogram is a graph showing arelationship between the yarn thickness variation period (cm) and thecoefficient of variation of the yarn thickness (CV %) of the thick andthin polyester multifilament yarn and prepared by the normal mode testmethod using the Uster evenness tester spectrograph (made by zellwegerUster Co., Switzerland) at a yarn speed of 400 m/min. The Usterspectrograph enables details of unevenness of the yarn to be quicklymeasured and analized, and is particularly useful for determining theperiod of the yarn thickness variation.

[0025] The theory and practice of the yarn thickness evennessmeasurement by the Uster evenness tester spectrograph are described indetail in ┌Theory and Practice of Unevenness┘, the Textile MachinerySociety of Japan, pages 255 to 372.

[0026] Spectrograms of examples of the thick and thin polyestermultifilament yarns of the present invention and the conventional thickand thin polyester multifilament yarns are shown in FIGS. 1 and 2,respectively and will be explained in detail below. FIG. 1 is aspectrogram of the thick and thin polyester multifilament yarn preparedin Example 1 which will be described hereinafter, and FIG. 2 is aspectrogram of a conventional thick and thin polyester multifilamentyarn. In a comparison of FIG. 1 with FIG. 2, a characteristic differencetherebetween resides in the number of peaks in the yarn thicknessvariation coefficient (CV %) appearing in the spectrograms. Namely, inthe thick and thin polyester multifilament yarn of the presentinvention, two peaks in CV % appear in the range of 50 to 150 cm of thelong yarn thickness variation period and in the range of 4 to 10 cm ofthe short yarn thickness variation period, and thus the thickness of theyarn is widely dispersed. Compared with this, in FIG. 2, only one peakappears in the short yarn thickness variation period of 4 to 10 cm andno peak appeared in the long yarn thickness variation period. Therefore,the thick and thin polyester multifilament yarn exhibits a more naturalspun yarn-like appearance than that of the conventional yarn.

[0027] When the thick and thin polyester multifilament yarn of thepresent invention is subjected to a normal mode test for evenness in thethickness thereof using the Uster unevenness tester, two peaks in CV (%)of the yarn appear in the resultant spectrogram of the yarn. A firstpeak (P_(max-1)) appears in the ranges of the yarn thickness variationperiod of from 4 to 10 cm, preferably 5 to 8 cm and a second peak(P_(max-2)) appears in the ranges of the yarn thickness variation periodof from 50 to 150 cm, preferably 80 to 120 cm. Also, the ratio(P_(max-1))/(P_(max-2)) of the first peak value (P_(max-1)) in CV % tothe second peak value (P_(max-2)) in CV % must be in the range of 1.0 to4.0, preferably 1.5 to 2.0. If the spectrogram shows only one peak in CV%., or at least one of the peaks appears outside of the above-mentionedspecific ranges of the yarn thickness variation period or the peak valueratio (P_(max-1))/(P_(max-2)) falls outside of the above-mentionedspecific range, the resultant thick and thin polyester multifilamentyarn exhibits a reduced random variance in distribution of the thickportions thereof and thus the natural fiber or filament yarn-like handof the resultant yarn is degraded or the dry touch and/or the spunyarn-like appearance of the yarn is deteriorated to an extent such thatthe purpose of the present invention is not completely attained.

[0028] In the spectrogram of the thick and thin polyester multifilamentyarn of the present invention, when the CV % value ratio(P_(max-1))/(P₂₀) of the first peak CV % value (P_(max-1)), as definedabove, to a CV % value (P₂₀) appearing at a yarn thickness variationperiod of 20 cm is in the range of 1.5 to 4.0, preferably 2.0 to 3.0,the resultant yarn advantageously exhibits improved natural fiber orfilament yarn-like hand, a dry touch and a spun yarn-like appearance.

[0029] In the thick and thin polyester multifilament yarn of the presentinvention, preferably, the thick portions of the individual filamentshave an length of 1 to 15 mm, more preferably 3 to 10 mm. If the thickportion length is too long, the resultant yarn may exhibit a degradednatural fiber or filament yarn-like hand, and if the thick portionlength is too short, the specific properties of the thick and thin yarnmay not be satisfactorily exhibited. Further, the thick and thinpolyester multi-filament yarn of the present invention preferably has anUster normal U % of 3.5% or more, more preferably in the range of 4.5 to8.0%.

[0030] The Uster normal mode U % is a mean yarn thickness unevennessrepresented by a ratio in % of the mean deviation to the mean value ofthe yarn thickness determined by the normal mode test method using theUster evenness tester at a yarn speed of 400 m/min. at a twist number of5500 turns/min. for one minute.

[0031] The U % value in the above-mentioned range enables both the roughtouch and the natural fiber or filament fabric-like hand of theresultant thick and thin polyester multifilament yarn fabric to berealized.

[0032] There is no limitation to the mean thickness of the individualthick and thin filaments and the average total thickness of the yarn.Usually, the mean thickness of the individual thick and thin filamentsis preferably 1.5 to 5.0 dtex and the mean total thickness of the yarnis preferably 40 to 170 dtex.

[0033] Also, there is no limitation to the cross-sectional profile anddimensions of the thick and thin individual filaments. A circularcross-sectional profile of the individual filaments may enable theresultant multifilament yarn to exhibit the natural fiber spun yarn-likeappearance. The thick and thin multifilaments having a triangularcross-sectional profile enable the resultant yarn to exhibit an enhanceddry touch and a spun yarn-like appearance.

[0034] The above-mentioned thick and thin polyester multifilament yarnof the present invention can be produced by, for example, the followingmethod.

[0035] An above-mentioned polyester is melted at a temperature of 280 to300° C., the polyester melt is extruded through a spinneret andsolidified by cooling; the resultant undrawn filaments were oiled withan oiling agent, and then interlaced in an interlacing apparatusprovided with three or more air-ejection openings through which airblasts were ejected under a pressure of 0.1 to 0.3 MPa toward the oiledundrawn filaments; the resultant interlaced undrawn filament yarn wassemi-drawn between a preheating roller having a periphery temperatureequal to or lower than the glass transition temperature of the polyesterand a drawing roller at a feeding speed on the preheating roller of 1500to 2500 m/min at a draw ratio of 1.1 to 1.5; and the semi-drawn filamentyarn was wound around a winder bobbin. Then, the wound semi-drawnfilament yarn was unwound and introduced at a feeding speed of 600 to1400 m/min into a drawing apparatus in which the fed semi-drawn filamentyarn is heated to a temperature of 80 to 110° C. on a periphery of apreheating roller and then to a temperature of 170 to 220° C. in anon-contact type heater, and then drawn at a draw ratio of 1.1 to 2.0 toprovide a thick and thin polyester multifilament yarn. Optionally, themultifilament yarn was further preheated to a temperature of 150 to 190°C. by a contact type or non-contact type heater and heat-set at a drawratio of 0.8 to 1.1.

[0036] In the process for producing the thick and thin polyestermultifilament yarn of the present invention, the first peak (P_(max1)),the second peak (P_(max2)) and the (P_(max1))/(P_(max2)) ratio can beadjusted by changing the conditions of the above-mentioned steps, forexample, the cross-sectional profile of the undrawn filaments in themelt-extruding step, the pressure of the air blasts applied to theundrawn filaments in the interlacing step, the draw ratio for theundrawn filaments in the semi-drawing step, the tension distribution onthe semi-drawn filaments on the pre-heating roller in the heat-settingstep and the draw ratio on the semi-drawn filaments in the heat-settingstep.

[0037] To produce a fabric from the above-mentioned thick and thinpolyester multifilament yarn of the present invention, the yarn isoptionally twisted at a desired twist number, and is woven or knittedinto a desired fabric structure. The fabric is optionally subjected to aweight reduction treatment with an aqueous alkali solution. The weightreduction treatment contributes to enhancing the spun yarn fabricappearance, the natural fiber or filament fabric-like appearance and thedry touch of the fabric to an extent that the conventional polyestermultifilament yarn fabric could not attain.

[0038] Since the present invention is intended to provide a thick andthin polyester multifilament yarn fabric having an enhanced spun yarnfabric-like appearance, a natural fiber or filament yarn fabric-likehand and a dry touch, the fabric preferably has a simple weave orknitting structure selected from, for example, plain weave structures,modified plain weave structures, simple twill weave structures, modifiedsimple twill weave structures, and satin weave structures, butcomplicated weave and knitting structures are not preferred for thefabric formed from the yarn of the present invention. The fabric is notlimited to a fabric consisting of the thick and thin polyestermultifilament yarn of the present invention in a content of 100%.However, the content of the yarn of the present invention in the fabricis preferably as high as possible, to enhance the spun yarn-likeappearance, the natural fiber or filament yarn fabric-like hand and thedry touch.

[0039] In another embodiment of the present invention, the thick andthin polyester multifilament yarn is a composite yarn comprising (A) aplurality of individual thick and thin polyester multifilaments havingan ultimate elongation (ELA) of 80% or more, an elastic recovery of 50%or less from 10% strain (elongation), a modulus of rigidity in stretch(EMA) of 5.89 GPa or less, a crystallinity (XpA) of 25% or more, ashrinkage in boiling water (BWSA) of 3% or less, and a thermal stress(TSA) at 160° C. of 0.44 mN/dtex and (B) a plurality of individual drawnpolyester filaments having an ultimate elongation (ELB) of 40% or less,a modulus of rigidity in stretch (EMB) of 7.85 GPa or more, a shrinkagein boiling water (BWSB) of 5% or more and a thermal stress (TSB) at 160°C. of 0.88 mN/dtex or more, the filaments (A) and the filaments (B)being intermingled with each other.

[0040] The intermingling of the filaments (A) with the filament (B) ispreferably effected by applying air blasts, jetted from an air jetfiber-intermingling apparatus, toward the filaments (A) and (B) parallelwith each other at room temperature.

[0041] Preferably, the thick and thin polyester filaments (A) have atriangular cross-sectional profile.

[0042] Also, the thick and thin polyester filaments (A) contain theabove-mentioned fine pore-forming agent.

[0043] In still another embodiment of the present invention, the thickand thin polyester multifilament yarn is a composite yarn produced byparalleling two or more types of undrawn polyester multifilament yarnsdifferent in natural draw ratio from each other; and drawing theparallel multifilament yarns at a draw ratio lower than the highestvalue and higher than the lowest value of the natural draw ratios of theparallel undrawn multifilament yarns.

[0044] In this embodiment, after the undrawn multifilament yarns areparalleled each other, the resultant undrawn yarn is subjected to afilament-intermingling procedure with air blasts jetted from an air-jetfiber-intermingling apparatus toward the undrawn yarn at roomtemperature, and then filament-intermingled yarn is drawn.

[0045] The undrawn polyester multifilament yarn having the highestnatural draw ratio preferably contains the above-mentioned finepore-forming agent.

[0046] The lowest value of the natural draw ratios of the undrawnmultifilament yarns to be paralleled each other is preferably in therange of from 1.1 to 1.7, more preferably 1.3 to 1.5. The highest valueof the natural draw ratios of the undrawn yarns is preferably 0.5 above,more preferably 0.7 above, the lowest value of the natural draw ratiosof the undrawn yarns, and is within the range of from 2.0 to 6.0.

[0047] In this embodiment, the intermingling ratio of the undrawnfilaments, different in the natural draw ratio from each other, to eachother, may be established in response to the desired properties and theuse of the resultant yarn. Preferably, the contents of the undrawnfilaments having a lowest natural draw ratio and the undrawn filamenthaving a highest natural draw ratio are 20% by weight or more,respectively. Particularly, the content of the undrawn filaments havingthe higher natural draw ratio is preferably higher than that of thelower natural draw ratio. Preferably, the ratio in content in weight ofthe undrawn filaments having the lowest natural draw ratio to theundrawn filaments having the highest natural draw ratio is in the rangeof 30/70 to 45/55. Also, in this embodiment, the composite yarn mayfurther comprise polyester multifilaments having a high shrinkage, forexample, of 15% or more in boiling water, in a content of 45% by weightor less.

[0048] Further, in this embodiment, the composite yarn may furthercomprise polyester multifilaments having a latent crimping property andbeing capable of crimping, when heated at a high temperature, forexample, 150° C. or more, in a content of 45% by weight or less.

[0049] The high shrinkage and/or polyester filaments mixed into thecomposite yarn enable the bulkiness of the resultant composite yarn tobe enhanced.

EXAMPLES

[0050] The present invention will be further illustrated by thefollowing examples which are merely representative and are not intendedto restrict the scope of the present invention in any way.

Example 1

[0051] A glass flask equipped with a refining distillation column ischarged with 197 parts by weight of dimethyl terephthalate, 124 parts byweight of ethylene glycol, 4 parts by weight of 3-carbomethoxy·sodiumbenzenesulfonate-5-sodium carboxylate (1.3 molar % based on the molaramount of the above-mentioned dimethyl terephthalate) and 0.118 part byweight of calcium acetate monohydrate; the charged reaction mixture wassubjected to a transesterification reaction at a temperature of 240° C.for 2 hours; after the resultant methyl alcohol is distilled off in astoichiometric amount, the remaining reaction product is placed in apolycondensation flask equipped with a refining distillation column andmixed with 0.112 part by weight of a stabilizer consisting of trimethylphosphate and 0.079 part by weight of a polycondensation catalystconsisting of antimony oxide; the resultant reaction mixture wassubjected to a polycondensation reaction at a temperature of 280° C.under the ambient atmospheric pressure of 20 minutes, then under areduced pressure of 3999.6 Pa (30 mmHg) for 15 minutes, and furtherunder a high vacuum for 80 minutes. The final inner pressure of theflask was 50.7 Pa (0.38 mmHg). The resultant modified polyesterexhibited an intrinsic viscosity of 0.640, determined inorthochlorophenol at a temperature of 35° C., and a softeningtemperature of 258° C.

[0052] After the reaction was complete, the resultant modified polymerwas pelletized, using a pelletizer.

[0053] The modified polymer pellets were dried at a temperature of 150for 180 minutes, and then melt-extruded through a spinneret having 36melt-spinning holes for undrawn filaments each having a triangularcross-sectional profile; the extruded filamentary polymer melt streamswere solidified by cooling; the resultant undrawn filaments were oiledwith an oiling agent, and then subjected to a interlacing procedure inwhich an interlacing apparatus equipped with three air-ejection nozzleswas employed, and three air blasts were jetted through the air-ejectionnozzles under a pressure of 0.15 MPa toward the undrawn filaments; theinterlaced undrawn filaments were taken up at a speed of 2250 m/min,semi-drawn at a speed of 3030 m/min, at a draw ratio of 3030/2250=1.35,and the semi-drawn filaments were wound around a wider roll.

[0054] The semi-drawn filament was unwound and drawn at a preheatingroller temperature of 87° C. and at a heat-setting heater (non-contacttype) temperature of 200° C., at a draw ratio of 1.4 at a drawing speedof 800 m/min. The drawn filaments were heat-set by a heat-setting heater(contact type) at a temperature of 175° C. at a draw ratio of 0.98, andthe heat set filaments were wound around a bobbin. The resultant thickand thin polyester multifilament yarn had a yarn count of 120 dtex/36filaments. The individual filaments of the yarn had a triangularcross-sectional profile.

[0055] The thick and thin multifilament yarn was subjected to aspectrographic test using the Uster unevenness tester and the U % testand to a measurement of shrinkage in boiling water for 30 minutes.

[0056] The test-results and measurement results are shown in Table 1.

[0057] A plain weave fabric (Habutue) was produced from warp and weftyarns each consisting of the above-mentioned thick and thin polyestermultifilament yarn. The plain weave fabric had a warp density of 86yarns/25.4 mm and weft density of 78 yarns/25.4 mm. The polyestermultifilament weave fabric was scoured, heat-set and subjected to aweight reduction treatment with an aqueous alkali solution in a weightreduction of 15%. Then, the fabric was subjected to an immersion dyeingprocedure with a blue-coloring disperse dye. The dyed fabric wasevaluated in dry touch, natural fiber or filament fabric hand and spunyarn fabric-like appearance.

[0058] The evaluation for each item was carried out by organolepticexamination of five skilled panelists, the evaluation results wereclassified into the following three classes. Class Panelist's evaluationresult 3 All panelists judged very good. 2 Three or more panelistsjudged good. 1 Three or more panelists judged bad.

[0059] The evaluation results are shown in Table 1.

Example 2

[0060] A thick and thin polyester multifilament yarn was produced andtested in the same procedures as in Example 1 with the followingexceptions.

[0061] In the interlacing step, the three air blasts were ejected undera pressure of 0.25 MPa toward the undrawn filaments.

[0062] The test results are shown in Table 1.

Example 3

[0063] A thick and thin polyester multifilament yarn was produced andtested in the same procedures as in Example 1 with the followingexceptions.

[0064] In the melt-extruding procedure, the spinneret had 36melt-spinning holes for undrawn filaments each having a circularcross-sectional profile.

[0065] The test results are shown in Table 1.

Comparative Example 1

[0066] A thick and thin polyester multifilament yarn was produced andtested in the same procedures as in Example 1 with the followingexceptions.

[0067] In the preheating step, the semi-drawn filaments were fed to thepreheating roller through a bending guide by which a variation intension on the filaments was generated.

Comparative Example 2

[0068] A thick and thin polyester multifilament yarn was produced andtested with the same procedures as in Example 1 with the followingexceptions.

[0069] In the heat-setting step, the draw ratio for the semi-drawnfilaments was 1.05.

[0070] The test results are shown in Table 1.

Comparative Example 3

[0071] A thick and thin polyester multifilament yarn was produced andtested with the same procedures as in Example 1 with the followingexceptions.

[0072] In the melt-extruding procedure, the melt-spinning holes each hada circular cross-sectional profile.

[0073] In the heat-setting procedure, the draw ratio for the semi-drawnfilaments was 1.05.

[0074] The test results are shown in Table 1.

Comparative Example 4

[0075] A thick and thin polyester multifilament yarn was produced andtested with the same procedures as in Example 1 with the followingexceptions.

[0076] In the interlacing step, the air blasts were applied under apressure of 0.05 MPa toward the undrawn filaments.

Comparative Example 5

[0077] A thick and thin polyester multifilament yarn was produced andtested with the same procedures as in Example 1 with the followingexceptions.

[0078] In the interlacing step, the air blasts were applied underpressure of 0.4 MPa toward the undrawn filaments.

[0079] The test results are shown in Table 1.

Comparative Example 6

[0080] A thick and thin polyester multifilament yarn was produced andtested in the same procedures as in Example 1 with the followingexceptions.

[0081] In the heat-setting step, the draw ratio for the semi-drawnfilaments was 2.1. TABLE 1 Item Thick and thin polyester multifilamentyarn Thick Shrinkage Fabric properties Period portion in boiling Cross-National Spun yarn Example P_(max1) P_(max2) P_(max1)/ P_(max1)/ lengthwater sectional Dry fiber fabric- fabric-like No. (cm) (cm) P_(max2) P₂₀(mm) (%) (%) profile touch like hand appearance Comparative 1 7 100 1.11.2 0.5 8.0 2.0 Triangle 2 1 1 Example 2 20  160 1.6 2.0 15 to 25  8.09.0 Triangle 1 1 1 3 20  160 1.6 2.0 15 to 25  8.0 9.0 Circle 1 1 1Example 1 7 100 1.6 2.0 3 to 12 5.5 5.5 Triangle 3 3 3 2 7 100 2.0 3.5 3to 12 5.5 5.5 Triangle 3 3 3 3 7 100 1.6 2.0 3 to 12 5.5 5.5 Circle 2 32 Comparative 4 7 100 0.8 1.2 3 to 12 5.5 4.5 Triangle 2 1 1 Example 5 7100 4.2 4.5 3 to 12 5.5 7.0 Triangle 3 1 1 6 3  70 1.2 1.5 3 to 12 5.53.5 Triangle 1 1 1

Industrial Applicability

[0082] The thick and thin polyester multifilament yarn of the presentinvention can be converted to a fabric having excellent natural fiberyarn-like hand, a dry touch and a spun yarn-like appearance which couldnot be exhibited by the conventional thick and thin polyestermultifilament yarn fabrics.

[0083] Also, when the thick and thin filaments contain a finepore-forming agent, the resultant thick and thin polyester multifilamentyarn fabric can be dyed to a high color density, has a good perspirationabsorbent property and a comfortable wearing property, and exhibits acotton fabric-like hand and appearance.

[0084] Thus, the thick and thin polyester multifilament yarn of thepresent invention has high industrial applicability.

1. A thick and thin polyester multifilament yarn comprising a pluralityof thick and thin polyester individual filaments the thickness of whichperiodically varies along the longitudinal direction thereof, whereinwhen the thick and thin multifilament yarn is subjected to a yarnthickness variation measurement, in the normal mode test method usingthe Uster evenness tester, the resultant spectrogram of the thick andthin multifilament yarn exhibits a first peak (P_(max1)) of thecoefficient of variation in yarn thickness at a thickness variationperiod of 4 to 10 cm and a second peak (P_(max2)) of the coefficient ofvariation in yarn thickness at a thickness variation period of 50 to 150cm, and the ratio (P_(max1)/P_(max2)) of the first peak coefficient ofvariation in the yarn thickness (P_(max1)) to the second peakcoefficient of variation in the yarn thickness (P_(max2)) is in therange of from 1.5 to 4.0.
 2. The thick and thin polyester multifilamentyarn as claimed in claim 1 wherein, in the spectrogram of the thick andthin multifilament yarn, a ratio (P_(max1)/P₂₀) of the first peakcoefficient of variation in the yarn thickness (P_(max1)) to acoefficient of variation in the yarn thickness, at a thickness variationperiod of 20 cm (P₂₀), is in the range of 1.5 to 4.0.
 3. The thick andthin polyester multifilament yarn as claimed in claim 1, wherein theindividual thick and thin multifilaments have thick portions having alength in the range of 1 to 15 mm, and the thick and thin multifilamentyarn has a Uster normal mode U %, which is a mean yarn thicknessunevenness represented by a ratio in % of the mean deviation to the meanvalue of the yarn thickness, of 3.5% or more, determined by the normalmode test method using the Uster evenness tester at a yarn speed of 400m/min at a twist number of 5500 turns/min for one minute.
 4. The thickand thin polyester multifilament yarn as claimed in claim 1, having ashrinkage in boiling water of 10% or less.
 5. The thick and thinpolyester multifilament yarn as claimed in claim 1, wherein theindividual thick and thin multifilaments each have a triangularcross-sectional profile.
 6. The thick and thin polyester multifilamentyarn as claimed in claim 1, wherein the individual thick and thinmultifilaments contain a fine pore-forming agent mixed into a matrixconsisting of a polyester resin.
 7. The thick and thin polyestermultifilament yarn as claimed in claim 6, wherein the fine pore-formingagent comprises a metal salt compound represented by the general formula(I):

in which formula (I), M¹, and M², respectively and independently fromeach other, represent a metal atom, R represents a hydrogen atom or anester structure-forming functional groups and n represents an integer of1 or 2.